Not really. Mutiny's passive is closer to Yorick, just it occurs on-kill instead of on every skill. Mutiny doesn't gain stats or a controllable pet with awesome stats... they aren't comparable at all beyond theme.

Possible suggestions for the skeleton crew!
A: Casting spells either extends the duration of active skeletons or resets it, allowing them to stick around longer.
B: Adding new skeletons extends the duration, to a limit.
C: Add a passive to one of his skills. I would suggest Cull to Arms, because it enhances the skill its self as well by making it easier to have multiple skeletons.

One thing, you say that the skeletons will prioritize his targets, but how else will they behave?
Even with just one person moving, it's pretty easy to get wedged between a wall of minions and have to stay there until they move.

Q: Most cones have some sort of secondary effect on them (Cho'gath's silence, Ashe's slow, or just damaging everything in range) and so this one seems kind of useless without an AD build. My suggestion would be to add some sort of utility to them (on-hit effects, move speed increase like galio's gust, small knockback) or just add an AP ratio to the damage.

W: looks good to me.

E: This one doesn't quite fit in with his motif. As an ability, it certainly works, but there doesn't really seem to be any reason for him to be screaming. my suggestions are either to have him deploy and stomp a barrel of gunpowder or take a swig of grog and belch black flames.

R: Being a whirlpool, you might consider adding a penalty/benefit for being in the middle. Either an area of increased damage or an "eye of the storm", where there is no damage, but to be there the enemy would have to be standing still.

Lore: Really F'ing awesome. My only qualm is that you say Gangplank found Mutiny, and that stories of the survivors got garbled. 1. After the token mention, Gangplank fades out. Seeing as he is officially the pirate king, I'd say he'd have something to say about this new (old?) player on the field. 2. Survivors. What happened? This is a good place to add something about his abilities, such as him skeletonizing a crew member and then calling his ghost ship to chase their ship around for awhile. Again with Gangplank; what's his account of the incident?

General: Seeing as he's pirate-themed, perhaps his weapons should not be a sword and gun. (solely for the purpose of being different from GP.) A hookhand, hatchet, or boathook would work here.

His skeletons behave like Elise's Spiderlings. Also, as an added precaution, like Yorick's Ghouls, they both ignore unit collision and will not obstruct other units.

Q) Firstly, it's not a cone: it's a very wide skill shot (wider than Trueshot Barrage, but obviously nothing close to the rage). I think it's utility is its raw pushing potential. Even if it were a cone, I'm not sure the champion needs extra utility even if it's standard for cones to offer utility.

E) It's not so much a scream-in-terror as a roar. It's Mutiny's Raise Morale, but in keeping with being dead. Belching flames is interesting though - they would definitely have to be blue flames, though.

Lore) Gangplank didn't find Mutiny. It specifically states that Gangplank was too busy, and so he sent someone else to find Mutiny. Gangplank doesn't appear again because this is Mutiny's lore (it's the same reasoning behind Warwick/Soraka's new lore). Mentioning his abilities/theme is an interesting ploy though - I'm going to tweak his lore such that few of the crew returned, and that those who remained met a worse fate than death. Or, perhaps, I'll just have Mutiny commandeer the ship and its crew - how did he get back to Bilgewater, after all? I'll contact the author, see if he can patch it up.

Also, to say "[Gangplank] is officially the pirate king" seems a bit overdone. There is no *official* pirate king. They are pirates!

General) He only uses a sword at current. The gun is sheathed, and never used except for his taunt (similar to Malzahar's knife). I had considered a hook though. His sword is closer to a broadsword/giant piece of metal, than Gangplank's cutlass, though.

This is one of those cases in which someone has followed the frame of champcrafting and it worked out in their favor (in case your wondering 3mpty refer to my AMA on ability synergy) while hes abilities do not synergize with each other per say, they do all work to accomplish the same goal, and his E synergizes with his Ultimate and his W with his passive, which is a break in the rule but a break done right. The rule is that they usually synergize with the Q, and ALL synergize with the passive, but this modification is an example of how to break the frame slightly and still have it work very well. His goal is very similar to Gankplank's, he is a chaser inherently, both of his utilies slow, I feel though that his W should give him a movement speed bonus in addition to what it already does. In short, for me, synergy works for him and he could be a very entertaining champion, however, as was said, he does need to have some of his abilities mentioned in either his lore or his judgement if you have one. This is key to bringing his synergy to his lore, or lore/ability synergy. It allows your readers to understand why he is what he is, and why he does what he does. It gives the readers a deeper understanding of his character. I shall feature this on my AMA.